The present invention relates to a jamming signal generating circuit for generating an interfering signal, which is employed in a CATV system. The CATV system has a distribution unit for distributing signals from a branching line to respective terminals. The distribution unit includes a central viewing control system for controlling subscriber viewing according to a subscriber payment program.
The present inventor has described such an apparatus which is a central viewing control system for a CATV system. For example, see Japanese Laid-Open Application No. 59-101600. In this system, the level of jamming signal is established at a fixed level and the jamming signal is produced at high speed.
However, because of the fixed establishment of the level of the jamming signal it is difficult to constantly maintain a desirable level ratio relative to any level condition of a television signal. Therefore, when the level ratio falls outside of the effective range, there is the disadvantage that the effect of scrambling decreases. Furthermore, as a result of the high-speed production of the jamming signal, an extremely high-speed responsive circuit is required when the level control is performed by AGC (automatic gain control).